This invention relates to hook-latch assemblies, and more specifically, to an adjustable, flush mounted, over center, hook-latch assembly of the general type used to secure abutting aircraft panels in place.
Over center, hook-latches are well known in this art. Examples can be found in U.S. Pat. Nos. 2,712,955; 2,695,803; 2,904,141, and 2,800,346. As can be readily seen, in these U.S. Patents, as well as undoubtedly in others, the fulcrum axis of the latch handle is mounted to a bracket aircraft structural panel, and the latch-hook engages a keeper on the abutting panel. When the latch handle is in its stowed position, adjacent the mounting service, and flush with the outer skin of the aircraft, the load on the latch hook creates a lever arm on the latch handle about the fulcrum axis in the direction which maintains the latch handle in its closed position. The distance between the latch hook and the keeper is critical and must be maintained at a proper torque setting. If the distance is too great, the latch will not close or will create excessive stress forces on the aircraft components causing possible damage on them as well as the hook-latch assembly. If, on the other hand, the distance is too close, the hook will not engage the keeper with sufficient tension to maintain the panels in abutting engagement, while in flight. The hook-latch assembly must include some type of adjusting means on the assembly to accurately adjust the hook relative to the keeper for their initial installation, and subsequently when stress to the aircraft structure, may change the relative positions of the hook and keeper.
Generally, prior art adjusting means required that the latch be released to adjust the relative position of the latch and keeper. Because proper adjustment could only be established when the latch and keeper are engaged, trial and error adjustment is necessitated. This becomes a time consuming task when a plurality of latches are utilized to abutt various aircraft structures, because of the numbers and possible interaction between the various fasteners on any pair of abutting surfaces.
Other prior art fasteners of this type, could only be adjusted from the under, or unexposed side of the aircraft abutting panels; requiring that the panels be removed, adjusted and then replaced time and again to provide proper tension or torque to a plurality of hook-latch combinations on one pair of abutting aircraft assemblies.
Other prior art fasteners, which could be adjusted while the latch was secured to the keeper from the outside, provided for moving or adjusting the latch arm pivot axis relative to the fulcrum axis of the latch handle. This required adjacent elongated slots extending in different directions which receive the pivot or fulcrum pin and a pair of yoke members for locating and securing the pivot pin within the slots, at a preselected vertical or horizontal position. This type of prior art fasteners is suscepticle to wear on the slot and connecting surfaces. The position of the pin is controlled by a single center positioned screw, which can cause the assembly to wobble at certain aircraft vibration frequencies, increasing the wear and reducing reliability of the fastener system. No means is provided in this type of fastening system for maintaining proper alignment of the abutting panels when latch wear is encountered causing relative side movement between the keeper and latch and considerable numbers of components are required to provide this type of assembly. In addition, this type of assembly is very susceptible to failure, due to the large number of active parts used in its construction.